Security: Hackers and industrial spies could exploit new ways to
break into systems.
Businesses and government establishments could be at risk from a
new eavesdropping technology that allows snoopers to read the
contents of computer screens and data devices through office
windows from a distance of up to 50m.
Scientists at Cambridge University have shown that they can
reconstruct images from a PC screen or read data from LED devices
by measuring tiny variations in the light they reflect through
office windows. Similar technology could be harnessed by
intelligence agencies or industrial spies to steal commercial or
government secrets from otherwise secure organisations, experts
said.
The technique, known as optical time-domain eavesdropping, is
analogous to the "tempest" phenomenon discovered in the 1980s,
which allows eavesdroppers to read data by tuning into
electromagnetic waves emitted by computer monitors.
But Markus Kuhn, a researcher at the university's computer
laboratory who discovered the phenomenon, said "optical tempest"
could be a more effective snooping technology than its
electromagnetic equivalent.
"It is a particular concern for organisations that have removed
other security risks and where there is a determined opponent, such
as an intelligence agency. Military organisations that use
cryptographic keys could be at risk," said Kuhn.
The technique relies on the fact that the pixels on computer
screens glow for a fraction of a second when they are struck by the
moving electron beam in the visual display unit (VDU). A
photodetector can pick up the tiny variations in light emitted and,
by averaging emissions over a few seconds, can accurately
re-construct the original screen image.
The technology is sensitive enough to reconstruct images from light
reflected from internal walls through a window or through frosted
glass. Eavesdroppers could use the same techniques to read
sensitive data by decoding the LED indicators used in transmission
devices in internal company networks.
"The main limitation is that the room has to be relatively dark. It
works well if there is no other light in the room, and it is
twilight outside - you can [read the screen] from 50m away," said
Kuhn.
Simple countermeasures are available, however. One approach is to
make sure that rooms are always well lit. Certain types of
fluorescent tubes can make eavesdropping difficult, if they emit
light with similar frequencies to a VDU. Another approach is to
replace VDUs with liquid crystal displays, which emit no
afterglow.
bill.goodwin@rbi.co.uk